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1.
The effect of divalent cation substitution on the structure and magnetic properties of La1.2Sr1.8-xCaxMn2O7 (x = 0-0.900) is investigated in this paper. Partly replacing divalent cation Sr2+ by Ca2+ ions results in the weakening and then disappearance of long-range ferromagnetic ordering, and the formation of spin canting and low-temperature spin-glass. Based on structural analysis by Rietveld profile fitting, we suggest that this variation of magnetic property be related to a Jahn-Teller-type attice distortion of MnO6 octahedra due to the introduction of the smaller sized Ca2+ ions.  相似文献   
2.
第一讲中子散射与散裂中子源   总被引:1,自引:0,他引:1  
中子散射是研究物质微观结构和动态的理想工具之一,广泛地应用于凝聚态物质研究和应用的众多学科领域.散裂中子源能是新一代的加速器基脉冲中子源,能为中子散射提供高通量的脉冲中子.文章简明地介绍了中子散射的特点和它作为物质结构和动态探针的优越性,以及散裂中子源的基本原理、发展状况和多学科的应用优势.我国计划建设的散裂中子源CSNS中,靶站将由多片钨靶、铍/铁反射体和铁/重混凝土生物屏蔽体组成.质子束功率100kW下,脉冲中子通量约为2.4×1016n/cm2/s.第一期将设计建造高通量粉末衍射仪、高分辨粉末衍射仪、小角散射仪、多功能反射仪和直接几何非弹性散射仪等五台典型的中子散射谱仪,以覆盖大部分的中子散射研究领域.  相似文献   
3.
We report on alloys formed by replacing iron with manganese in the compound Dy2Fe17C1.0 Samples were characterized by X-ray diffraction and magnetic measure-ments, The 2:17-type structure can be crystallized in the whole range of manganese substitution. The Curie temperature of the series of Dy2Fe17-xMnxC1.0(x= 0-17) drops down considerably from 515K for x = 0 to about 20K for compounds with high manganese concentration, and the compensation point was observed in a narrow range of x≈4-6. The rapid decrease of the magnetization shows that the manganese substitution is not a simple magnetic dilution to the transition-metal sublattice mo-ment, it indicates that the moment of Mn may be antiparallel to that of Fe. The field dependence of the magnetization of Dy2Fe17-xMnxC1.0 may indicate the existence of the nonlinear magnetic structure for the samples with high Mn conoentrations.  相似文献   
4.
The crystal and magnetic structures of Nd2Fe14Si3 at room temperature were refined by Rietveld analysis of neutron-powder-diffraction data. It was found that silicon atoms occupy preferentially both 18h and 18f of Th2Zn17-type structure with occupancies 0.36 and 0.14, respectively, The Fe-Fe bond-lengths computed with the refined crystallographic parameters have optimum values, as compared with those of Nd2Fe17 compounds, which can explain well why the Curie temperature rises strongly when the unit cell volume reduces with the substitution of silicon for iron in Nd2Fe17.  相似文献   
5.
In this paper, the effect of divalent cation substitution on the structure and magnetic properties in La2-2xSr1Ca2xMn2O7 have been investigated systematically using bulk samples with a wide doping concentration range 0.25≤x≤1.00. Replacing trivalent La ions by divalent Ca ions results in the weakening and then disappearance of the long-range ferromagnetic (FM) ordering, the formation of spin canting, antiferromagnetic (AFM) ordering and low-temperature spin-glass. These results show that increasing the hole-doping concentration significantly suppresses the FM state. We suggest that this variation of magnetic properties is related to the competition of the FM and AFM interactions resulting from the change of Mn3+/Mn4+ ratio and Jahn-Teller-type lattice distortion of MnO6 octahedra due to the introduction of Ca2+ ions.  相似文献   
6.
YBa2Cu3O6+δ的高频模及其随氧含量δ的变化   总被引:2,自引:0,他引:2       下载免费PDF全文
在中国原子能科学研究院新建的宽角(~30°)Be过滤探测器中子非弹性散射谱仪上,在入射中子能量从10直至150meV的范围内,测量了几种不同氧含量的YBa2Cu3O6+δ样品的中子非弹性散射能谱。结果表明:(1)在δ=0和0.2时,在60至150meV能量范围内,发现有强的高频模存在,当其温度高到Nel点(~410K)以上直至466K时,没有观察出高频模强度的减弱。而δ=0.78和0.97时,在75至150meV能量范围内,散射强度在测量误 关键词:  相似文献   
7.
This paper investigates the single-molecule magnets of pure and Cr/Fe-doped Mn12-Ac. The components of the mixed crystals are identified by AC susceptibility technique. The ground-state spin and anisotropy parameters of doped Mn12-Ac are obtained: (i) MnllCr-Ac (S=19/2, D=0.62K, B=0.0009K, A=63K), and (ii) Mn11Fe-Ac (S=21/2, D=0.39 K, B=0.001 K, △=55 K). The single-ion origin of the magnetic anisotropy is discussed.  相似文献   
8.
通过磁性测量、Mossbauer谱和中子衍射研究了室温下Pr6Fe13Ge的磁结构 .磁性原子集中分布在z=0和z=1 / 2镜面的两侧 ,被z=1 / 4 ,3/ 4处的非磁性原子分割成M(磁性 ) /NM(非磁性 ) /M(磁性 )排列的三明治结构 .磁性层M内磁矩为共线铁磁耦合 ,磁矩方向少量偏离ab面 ,形成小的c轴方向的分量 ;层与层之间 ,ab面内的磁矩分量为反铁磁耦合 ,而c轴方向的分量为铁磁耦合  相似文献   
9.
The superconductivity of a sintered pellet of the newly discovered MgB2 superconductor has been studied with magnetic measurements and its crystal structure was analysed using the Rietveld method of powder X-ray patterns. It has hexagonal symmetry (S.G. P6/mmm) with unit cell lattice parameters a=0.308136(14)nm and c=0.351782(17)nm.  相似文献   
10.
碳含量对Y-Ni-B-C超导相的形成与临界温度的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
报道ThCr2Si2型结构的四元金属间化合物Y2Ni2B2Cx的形成与超导电性.当碳配比含量x=0.9—1.2时,电弧熔炼的合金结晶为较好的YNi2B2C单相.当x<0.8或x>1.2时,合金中虽仍以YNi2B2C为主相,但杂相明显增加.超导转变温度Tc随碳含量增加明显分为两个台阶.x≤0.8时,Tc约为12.5K;x≥0.9时,Tc约为15K. 关键词:  相似文献   
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